Biomass, a basic product of agriculture, is one of the main sinks of carbon in global cycle. Additionally, it can be used as a renewable source of energy, leading to depletion in CO2 emissions. The paper presents the results of estimations on the current and potential share of catch crop cultivation in climate change mitigation, in Poland, where the agricultural sector plays a significant economic role. The estimation of CO2 assimilation in biomass was performed on the basis of our own data on yields of commonly used catch crops, obtained in randomly selected 80 farms in Poland, and the content of carbon in the biomass. Calculation of energy potential of the biomass was conducted, assuming its conversion into biogas, on the basis of our own data on catch crop yields and the literature data on their biomethane potentials. The results have shown that catch crops in Poland, which are cultivated to an area of 1.177 mln ha sequestrate 6.85 mln t CO2 yr−1. However, considering the total area of fields used for spring crop cultivation, it is possible to increase the sequestration to 18.25 mln t CO2 yr−1, which constitutes about 6% of the annual emission of CO2 in Poland. Biomethane yields per hectare of particular crops ranged from 965 to 1762 m3 CH4 ha−1, and were significantly lower compared to maize, which is commonly in use in biogas plants. However, due to high biomethane potential and favorable chemical composition, catch crops can be a valuable co-substrate for the feedstocks with a high C:N ratio. The potential recovery of energy produced from aboveground biomass of catch crops harvested in Poland during the year is 6327 GWh of electricity and 7230 GWh of thermal energy. Thus, it is advisable to promote catch crops on a wide scale due to substantial environmental benefits of their cultivation.